Updated at 12:06 p.m. ET
President Trump's defense team is expecting to use only two to three hours on the Senate floor on Tuesday to finish laying out their case against impeachment, a source familiar with the legal team's thinking told NPR's Tamara Keith.
Trump's lawyers, which began their arguments Saturday, had 24 hours over three days to make their case — the same time given to the Democratic House impeachment managers who presented their arguments against the president last week.
Watch the proceedings live here.
Before the final day of Trump's defense began, Senate Minority Leader Chuck Schumer, D-N.Y., made it clear that Democrats were not interested in any deal to call witnesses that involved former Vice President Joe Biden's son Hunter.
"Hunter Biden has nothing to do with the facts of this trial," Schumer said at a press conference Tuesday morning.
Schumer insisted that senators should hear from the same four witnesses that he has been pushing for since the start of the trial — former national security adviser John Bolton; acting White House chief of staff Mick Mulvaney; Robert Blair, a White House official; and Michael Duffey, an official at the Office of Management and Budget.
"Were not bargaining with them — four witnesses and four sets of documents," Schumer said.
He also dismissed a proposal floated by GOP senators Lankford and Graham to allow Senators to read Bolton's manuscript in the secure room in the Capitol ("SCIF"). He called this idea "absurd."
"Its a book. There's no need for it to be read in the SCIF unless you want to hide something."
Shortly before winding down Monday night's arguments in the Senate impeachment trial of President Trump, defense lawyer Alan Dershowitz addressed the elephant in the room: whether potential testimony from Bolton would alter the course of the proceeding.
The New York Times reported Sunday evening that Bolton wrote in a forthcoming book that the president told him in August he wanted to continue withholding close to $400 million in military assistance to Ukraine until that country's government agreed to launch investigations of former Vice President Joe Biden and his son Hunter.
Dershowitz was the first member of the president's defense team to directly acknowledge how recent Bolton news had consumed Washington, as speculation raged over the Senate possibly calling him as a witness.
Bolton's possible firsthand account of the events at the heart of the impeachment trial? Not necessary, argued Dershowitz.
"Nothing in the Bolton revelations, even if true, would rise to the level of an abuse of power or an impeachable offense," he said.
Democrats need to persuade at least four Republicans to defect from their party's leadership in order to support a subpoena of Bolton, a threshold that Sen. Mitt Romney, R-Utah, said on Monday appeared "increasingly likely."
Sen. Angus King, I-Maine, told NPR on Monday that he, too, believes the Senate is now inching closer to having enough votes to bring Bolton into the chamber for live testimony.
"I'm already hearing a number of Republicans who are moving toward voting to at least hear from John Bolton, if not other witnesses," he said.
"I think there'll be more," said King, referring to the four GOP votes that Democrats need to call Bolton. "My bold prediction will be five or 10."
The House impeachment articles accuse Trump of abuse of power for asking Ukraine to announce investigations into his political rivals, allegedly using $391 million in vital security assistance to pressure the country into launching the probes. The House articles also charge obstruction of Congress for the White House's refusal to cooperate with impeachment investigators.
But on Monday, Trump's defense team offered vastly different version of events, arguing that the president's freezing of military aid was done out of a legitimate concern over corruption in Ukraine, pointing out that the congressionally approved funding was eventually released.
Eric Herschmann, another Trump defense lawyer, maintained that the holdup in military aid was not as consequential as Democrats have portrayed it to be.
"It is absurd on its face. Not one American life was in jeopardy or lost by the short delay, and they know it," Herschmann said.
Ken Starr, who is defending Trump and who led the investigation into President Bill Clinton that triggered Clinton's impeachment, made the case that Trump's impeachment, the third in American history, shows that "we are living in what aptly can be described as the age of impeachment," adding the process is "filled with acrimony and divides the country like nothing else."
"Like war, impeachment is hell, or at least, presidential impeachment is hell," he said.
The defense team also used Monday to attack the Biden family, playing a television interview with Hunter Biden answering questions about his time as a board member of the energy company Burisma when his father was vice president.
Trump defense lawyer Pam Bondi, the former attorney general of Florida, ran through a long timeline of events suggesting that Hunter Biden's involvement with Burisma was questionable enough to justify Trump's concerns about possible corruption.
Neither Joe Biden nor his son have been accused of any wrongdoing connected to Ukraine and Burisma.
Yet Bondi cited news outlets that have covered the Bidens and the energy company before saying: "They all thought there was cause to raise the issue about the Bidens and Burisma."
Added Bondi: "The House managers might say, without evidence, that everything we just said has been debunked, that the evidence points entirely and unequivocally in the other direction. That is a distraction."
"They don't believe that there was any concern to raise here," she said. "And all we're saying is that there was a basis to talk about this, to raise this issue."
Andrew Bates, a spokesman for Joe Biden, characterized Bondi's presentation as a "conspiracy theory" that has been "conclusively refuted."
"Joe Biden was instrumental to a bipartisan and international anti-corruption victory. It's no surprise that such a thing is anathema to President Trump," Bates said in a statement.
Meanwhile in the Senate, lawmakers struggled on Monday to push through the daylong presentations by Trump's legal team.
Senators appeared more worn down than last week, giving way to yawns or strolls into the cloakroom for extended breaks.
Once Trump's legal team rests, the trial will then move to the questions phase in which senators submit in writing questions to the prosecution or defense that the Chief Justice John Robert will read aloud.
After the questions wrap up, senators will then take up whether to call witnesses.
Rep. Adam Schiff, D-Calif., the lead House impeachment manager, has said that the White House's attempt to block witnesses from the impeachment process is proof of a cover-up. On Monday, Schiff added to those contentions, saying on CNN that lawmakers interested in fully assessing the impeachment charges should want to hear Bolton's side of the story.
"I don't know how you can explain that you wanted a search for the truth in this trial and say you don't want to hear from a witness who had a direct conversation about the central allegation in the articles of impeachment," Schiff said.
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